The spinal cord provides sensory and motor innervation to the neck, torso, and limbs. Sensory information from the skin, muscles, joints, and some internal organs is relayed to the spinal cord by sensory neurons whose cell bodies are located in the dorsal root ganglia (DRG) that lie immediately adjacent to the spinal cord. That sensory information is routed to neural networks in the spinal cord and brain, contributing directly to the formation of conscious sensory experiences (i.e., perception) and to the regulation of motor and autonomic functions. In contrast, the ventral nerve roots that emanate from the spinal cord convey efferent information to the periphery. While information from these sensory neurons would be very useful for patients with various neurological disorders, there are no practical technologies for continuous long-term monitoring of such sensory signals.
Functional electrical stimulation (FES) of efferent pathways provides a mechanism for the direct control of musculoskeletal, respiratory, bladder, rectal, and sexual function after brain and spinal cord injury. Further, electrical stimulation of afferent pathways can be used to provide a mechanism for the control of muscle, bladder, rectal, and sexual function after brain and spinal cord injury, by leading to reflex activation of spinal circuits and recruitment of efferent pathways. However, current FES applications operate mainly in an open-loop mode, without automatic regulation or biological input to modulate the stimulation, and continuous feedback control has yet to be fully implemented in most FES applications due to multiple challenges. Further, current methods for activating afferents activate an entire nerve or nearby nerves and thus other undesired functions, are likely to occur.